Railroad coil cars are used to transport coiled materials, most typically coils of steel sheet. Coils can be carried with their coiling axes of rotation (that is, the axes of rotation about which the coils are wound) oriented longitudinally, that is, parallel to the rolling direction of the car. The coils are generally carried in a trough, or troughs, mounted on a railcar underframe. The troughs are generally V-shaped and have inwardly inclined surfaces that support the coil. The troughs are typically lined with wood decking to provide cushioning for the coils. When a coil sits in a trough, the circumference of the coil is tangent to the V at two points such that the coil is prevented from rolling.
A coil car may have single, double or triple longitudinally extending troughs. The use of multiple troughs allows any single car to carry either a load of large coils in the center trough or a load of relatively smaller diameter coils, or coils of various diameters such that lading more closely approaches maximum car capacity during a higher percentage of car operation. Additionally, some coil cars have been provided with trough assemblies that can be shifted to permit conversion between different trough modes. An example of a coil car that can be converted from a single to a double trough mode can be found in U.S. Pat. No. 3,291,072, issued to Cunningham on Dec. 13, 1966. Similarly, conversion of a coil car from a single or triple trough arrangement to a double trough mode is shown in U.S. Pat. No. 4,451,188, issued to Smith et al., on May 29, 1984. The general object is to provide versatility such that overall car utilisation is improved. Hence, the car is more economically attractive to a user.
Historically, coil cars have been constructed on a flat car underframe having a through-center-sill, that is, a main center sill that runs from one end of the rail car to the other. In this type of car the center sill serves as the main structural member of the car and functions as the primary load path of the car both for longitudinal buff and draft loads from coupler to coupler, and for carrying the vertical load bending moment between the trucks. The trough structure, or bunk, is mounted on the flat car deck. In such a car the cross-bearers carry loads into the main center sill. The side sills tend to be relatively small, and serve to tie the outboard ends of the cross-bearers together. Conventionally, the center sill is box-shaped in cross-section. That is, it is rectangular and has a constant depth of section. The top and bottom flanges of the main center sill tend to be very heavy in such cars, since they are relied upon to carry the vertical bending load.
Alternatively, another way to construct a coil car having a triple trough arrangement employs a central trough supported by a main center sill and an array of laterally extending cross-bearers and cross-ties that are angled upward and outward in a V-shape. At their distal end the cross-bearers and cross-ties meet, and are tied together by, relatively small side sills in a manner generally similar to a flat car. A central trough extends longitudinally above the center sill with side troughs lying outboard of the central trough. The side troughs are formed using slanted decking and are mounted above the cross-bearers at about the same height as the central trough relative to top of rail. In this arrangement the center sill is still relied upon to carry the great majority of the bending load.
Coil cars can also be fabricated as integrated structures. One way to do this is to employ a deep center sill, elevated side sills, and substantial cross-bearers mounted in a V between the center sill and substantial, load bearing side sills. The cross bearers and trough sheets carry shear between the side sills and the center sill. In this way the structural skeleton of the car acts in the manner of a deep V-shaped channel with flanges at each toe, namely the side sills, and at the point of the V, namely the center sill. In this arrangement, under vertical bending loads, the side sills are in compression, and the main sill is in tension.
In the cases of either a V-shaped integrated structure, or even a traditional flat car based structure, it may be beneficial to employ a “fish belly” center sill. A fish belly center sill is a center sill that is relatively shallow over the trucks, and has a much deeper central portions in the longitudinal span between the trucks. It is advantageous to have a deeper section at mid-span where the bending moment due to vertical loads may tend to be greatest.
Another way to achieve a greater depth of effective section in an integrated structure, so that a higher sectional second moment of area is obtained, is to employ deep side sills, in a manner akin to a well car. The deep side sills act as longitudinal beams. A longitudinal cradle, namely the trough structure, is hung between the side sills. In this kind of car, the main longitudinal structural members are the side sills which carry the great majority of the bending load. The cradle itself may have a center sill to tie the cross-bearers together at mid-span between the side sills. A center sill of modest proportions is sufficient for this purpose. The side sills carry the load back to main bolsters, and then into the draft gear mounted longitudinally outboard of each truck.
Where deep side sills are used, the minimum height of the bottom chord of the side sill is determined by the underframe portion of the design envelope prescribed by the AAR, such as for AAR plate B, plate C, or such other plate as may be applicable. At lower heights, the allowable width of the car diminishes, so the overall width of the car measured over the side sill bottom chords needs to be relatively narrow as sectional depth increases. Conversely, to accommodate the largest possible load width, it may tend to be desirable for the top chords of the side sills to be spread as far as possible within the allowable car width of 10′-8″. Thus it may be beneficial to locate the bottom chord closer to the car centerline than the top chord.
It may be desirable to be able to carry steel coils in a side-by-side arrangement. If three troughs are provided, it is advantageous for the center trough to be carried at a different height, relative to top of rail (TOR), than the outboard, or side, troughs. This may be beneficial for at least several reasons.
First, the total width of lading that can be carried by a coil car at one time is limited by the allowable car width envelope. If three identically sized coils are mounted such that the axes of the coils are carried at the same height relative to top of rail, then the sum of the diameters of the coils, plus the necessary clearance between coils, is limited by the maximum allowable coil car lading width. However, if the coiling axis of rotation of one coil is higher than an adjacent coil of equal or lesser diameter, then it may be possible to carry the coils in a partially encroaching, or overlapping, arrangement. That is, a greater sum of diameters may be accommodated than would otherwise be possible within the nominal maximum loading width. As a result, lading can include a combination of larger coils than might otherwise be possible, thus tending to improve car capacity utilisation.
Second, it is desirable that the point of maximum width of the load be carried at a height that is greater than the height of the uppermost extremity of the top chord members of the side sills. Once again, the advantage of this is that, generally, this will allow the vertical projection of the outboard coil to encroach more closely to the inner edge of the top chord, and so permit a larger coil to be carried in the outboard trough. This condition may be reached when the car is carrying two coils in excess of 40 inches in diameter side by side, with the central trough either empty, or carrying a relatively small coil, such as a coil of rather less than 30 inches in diameter. Since the second moment of area of the primary load bearing structure varies strongly with the depth of section, it is better for the side sill top chord to be carried at a relatively high level. Since the height of the top chord is related to the height of the outboard trough, an increase in elevation of the outboard trough by even a few inches is advantageous.
Third, in terms of car versatility, it is advantageous to be able to carry a variety of loads, whether a single very large coil in the central trough, two medium sized coils side-by-side in the outside troughs, or three somewhat smaller coils in each of three troughs. In general, the larger the central trough, the smaller the outboard troughs. If the outboard troughs are raised relative to the central trough, the overall trough capacity, and hence car versatility, will be increased. That is, a car with a central trough capable of accommodating a 74 inch coil, may only be able to accommodate 36 inch coils in the outboard troughs when the central trough is empty if the troughs are all carried at the same height. However, if the outboard troughs are carried at a higher level, then it may be possible to carry outboard coils of greater diameter, such as 44 or 48 inches, when the central trough is empty.
Reference is made herein to troughs being carried at the same, or different, heights relative to top of rail, commonly on an assumption of troughs of generally similar geometry. For the purposes of this description, each of the troughs has planar sloped side sheets. The planes of the opposed side sheets meet at some line of intersection parallel to the longitudinal center line of the car, the line of intersection lying at some height below the flat bottom of the valley of the trough. In structural terms, the difference in the height at which one trough is carried relative to another trough can be taken by comparison of the heights of the flat bottoms of the valley, since the bottom height may tend to be defined by the upper flange of a longitudinally extending structural member.
Reference can also be made to the height at which the centerlines of coils of the same size would lie for the various troughs. This is not a function of the height of the bottom of the valley, but rather of the height of the line of intersection of the planes of the slope sheets (assuming them to be planar), and the angle of the slope sheets. Once the angle of slope has been chosen, the difference in height of the flat bottom of the valley relative to the line of intersection of the planes is determined by the minimum diameter of coil to be carried, which will, with allowance for clearance, fix the width of the flat bottom. For troughs having the same angle of slope and the same bottom height, a narrow bottom will force a coil to be carried relatively higher than a wide bottom. Similarly, for bottoms of the same height and width, a steep slope will force a coil to be carried higher than a shallow slope.
The slope of the trough is an important design parameter. Whether for single or multiple trough cars, it is generally desirable that a coil not be able to escape from the trough during cornering. One standard is that a coil should not escape under a 0.45 g lateral load as a condition for general interchange service. This implies a trough slope of about 24.2 degrees measured from the horizontal. At least one rail road company has indicated that a slope of 23 degrees is acceptable for its purposes. It is also desirable for the troughs to have some allowance for lateral tilting or swaying of the cars during lateral loading, such as 2 or 3 degrees. This implies a desirable trough angle of about 27 degrees, (namely, 24 plus 3). Trough width is a function of the chord length between the points of tangency of the largest coil to be carried to the opposed trough sheets. Consequently, as the trough slope angle decreases, the trough width decreases. Similarly, as slope angle increases, the trough becomes wider. However, as noted above, the sum of the widths of the troughs is limited by the plate B envelope, less the widths of the side sills and a clearance dimension between the side sills and the coils, and between adjacent coils.
For trough width maximisation, it is advantageous for the side sills to be carried close to the design envelope lateral boundaries. For interchangeable service, the lateral boundaries are defined by AAR plate B, with a width of 128 inches. In the past, coil cars have carried walkways outboard of the side sills of the trough cradles. It is advantageous not to have walkways that would extend beyond the plate B limit. One inventor has suggested using folding walkways that can be moved to a retracted position within the side sills. It would be advantageous to employ fixed walkways that do not require moving mechanisms.
Another rail road requirement has been for a restraining device, called a coil stop, to prevent longitudinal displacement of the coils during operation. Typically, a coil stop is a transversely oriented beam, or movable bulkhead, located in position across the trough after a coil has been loaded. The coil stop extends between the side sills and can be moved to a location near to a seated coil. The coil stop is then releasably, or removably anchored, typically with pins that locate in perforated strips mounted to the side sills. Shims are then inserted between the coil stop and the coil to give a snug fit. One design criterion suggests that the restraining device bear upon the coil at a height that is at least as high as the horizontal chord that subtends an arc of 108 degrees of the largest coil the trough is capable of carrying.
It is possible to use a coil stop bar retaining strip that extending laterally inboard of the side sill. However, it is generally desirable to trim the coil stop engagement strip back to increase the capacity of the outboard troughs. To this end, alternative embodiments of coil stop are described. In one embodiment, a horizontal pin is used to engage a strip mounted to a side web of the top chord of the side sill. In another embodiment vertical pins of the coil stop engage perforations in a horizontal strip placed within the vertical profile of the top chord.
Since coil stops are relatively heavy, it would be advantageous to provide a coil stop that is designed to be moved more easily from place to place along the troughs of the car. It would be advantageous to employ rollers, or a slider, for this purpose. Ease of adjustment can also be enhanced by reducing the weight of the coil stop, such as by removing material from the horizontal coil stop web.
When outboard troughs are used, as in a triple trough arrangement, it is advantageous for a longitudinal stringer to tie adjacent cross-bearers together along the spine, or groin, of the outboard troughs. Where the cross-bearer has a web and an upper flange defining the slope of the trough sheets, the stringer, such as a hollow section, can be located in a relief formed in the cross-bearer web. The bottom of the trough so formed may also provide a walkway space. When the bottom of the trough is used as a walkway, it may be advantageous for the coil stop to be provided with climbing means, such as a step, or stile, and handgrabs.